Narrow-channel Heat Exchangers have received diversified research and application interests due to the miniaturized geometry, elevated heat transfer characteristics, and better energy efficiency. Automatic Transmission Fluid (ATF) cooling is one of the most important challenges in recent automotive industries due to the quick response to thermo-physical properties with temperature variations. Although a wide range of investigation on characterization of heat transfer and fluid-flow in Minichannel Heat Exchanger (MICHX) for various fluids is available, literatures examining ATF heat transfer and Fluidflow behaviors in the MICHX are scarce. In the current study, attempts have been made to justify the suitability of MICHX application in cooling of ATF. Experimental investigations have been conducted in a well-equipped closed loop integrated thermal wind tunnel test facility using wavy finned-MCHX as a test specimen. The inlet temperature of the ATF was maintained at a constant 75°C throughout the experiment. Air velocities of 6, 10, 14 and 18 m/s were applied. The entering air temperatures were varied at 15, 22, 29, 36 and 43°C while ATF Reynolds number was varied from 3.00 to 30.00 within the air temperature range.The effects of ATF Reynolds number on heat transfer coefficient, and Nusselt number, as well as Heat Exchanger effectiveness-NTU for the air-flow Reynolds number of 1450-5200, were examined. ATF Nusselt number correlation with Reynolds number and Prandtl number was established as a power-law function while considering a variable property ratio. The analysis showed an enhanced result in heat transfer characterizations and good agreement with established phenomena of the multi-port Minichannel Heat Exchanges in open literature.